High frequency electric motor or generator including magnetic cores formed from thin film soft magnetic material

ABSTRACT

A device such as an electric motor, an electric generator, and a regenerative electric motor includes a plurality of independent energizable electromagnetic assemblies. Each independent electromagnetic assembly has an associated one-piece magnetic core formed from thin film soft magnetic material. Each independent electromagnetic assembly defines two stator poles located at opposite ends of the one-piece magnetic core. Each one-piece magnetic core provides the entire magnetic return path for the two opposite magnetic stator poles associated with each independent electromagnetic assembly.

BACKGROUND OF THE INVENTION

The present invention relates generally to electric motors, generators,and regenerative motors. The term regenerative motor is used herein torefer to a device that may be operated as either an electric motor or agenerator. More specifically, the invention relates to an electricmotor, generator, or regenerative motor including a stator arrangementwhich itself includes a plurality of individual electromagneticassemblies with each independent electromagnetic assembly including anassociated one-piece magnetic core formed from thin film soft magneticmaterial.

The electric motor and generator industry is continuously searching forways to provide motors and generators with increased efficiency andpower density. For some time now, it has been believed that motors andgenerators constructed using permanent super magnet rotors (for examplecobalt rare earth magnets and Neodymium-Iron-Boron magnets) and statorsincluding electromagnets with magnetic cores formed from thin film softmagnetic material have the potential to provide substantially higherefficiencies and power densities compared to conventional motors andgenerators. Also, because cores formed from thin film soft magneticmaterial are able to respond to changes in a magnetic field much morequickly than conventional ferrous core materials, magnetic cores formedfrom thin film soft magnetic material have the potential to allow muchfaster field switching within motors and generators, and therefore allowmuch higher speed and better controlled motors and generators thanconventional ferrous cores. However, to date it has proved verydifficult to provide an easily manufacturable motor or generator thatincludes magnetic cores formed from thin film soft magnetic materials.Furthermore, the configurations that have been disclosed to date do nottake full advantage of the capabilities of these potentially moreefficient materials for certain types of applications.

Thin film soft magnetic materials such as amorphous metal are typicallysupplied in a thin continuous ribbon having a uniform ribbon width. Inthe past, amorphous metal cores have been formed by rolling an amorphousmetal ribbon into a coil, annealing the winding, and then saturating andencapsulating the winding using an adhesive such as an epoxy. However,this material is a very hard material making it very difficult to cut orform easily, especially once it has been laminated into a bulk piece.Also, once annealed to achieve peak magnetic properties, these materialsbecome very brittle. This makes it difficult and expensive to use theconventional approach to constructing a magnetic core.

Another problem with amorphous metal magnetic cores is that the magneticpermeability of amorphous metal material is reduced when it is subjectedto physical stresses. This reduced permeability may be considerabledepending upon the intensity of the stresses on the amorphous metalmaterial. As an amorphous metal magnetic core is subjected to stresses,the efficiency at which the core directs or focuses magnetic flux isreduced resulting in higher magnetic losses, reduced efficiency,increased heat production, and reduced power. This phenomenon isreferred to as magnetostriction and may be caused by stresses resultingfrom magnetic forces during the operation of the motor or generator,mechanical stresses resulting from mechanical clamping or otherwisefixing the magnetic core in place, or internal stresses caused by thethermal expansion and/or expansion due to magnetic saturation of theamorphous metal material.

In U.S. Pat. Nos. 5,982,070 and 6,259,233 that issued to the applicantand that are both incorporated herein by reference, certain methods andarrangements for constructing electric motors and generators weredescribed. In these patents, hereinafter referred to as the '070 patentand '233 patent respectively, multiple amorphous metal core pieces aresupported in a dielectric housing to form an overall amorphous metalcore. Another U.S. Pat. No. 4,255,684 issued to Mischler et al.describes another motor configuration that utilizes amorphous metalmaterials. Although these approaches allow motors and generators to beconstructed using amorphous metal cores, there are some inherentproblems associated with these approaches. For example, the use ofmultiple core pieces to form the overall core means that there areparasitic gaps between adjacent core pieces that the magnetic flux hasto cross as the flux flows through the magnetic core. These parasiticgaps occur at any point that the flux must pass from one piece or layerof core material to another. Although these gaps may be made very smallby manufacturing the various core pieces to very tight tolerances, andmay be filled with epoxy, they still result in parasitic losses thatreduce the efficiency at which the flux can flow through the corecompared to a core that does not have these gaps.

In addition to the parasitic gap problem, the methods and arrangementsof the '070 and '233 patents make it difficult to always orient theamorphous metal magnetic material in the proper orientation. This isespecially true of the radial gap devices disclosed in these patents.The proper orientation of the thin film soft magnetic material isimportant to maximizing the efficiency at which the magnetic flux isable to flow through the core material, and therefore, the efficiency ofthe device.

In the case of the axial gap configurations disclosed in the '070 and'233 patents, the physical configuration of the axial gap device makesit difficult to maintain the proper air gap between the rotor and thestator. Because the magnetic forces act axially along the rotationalaxis of the device, expensive bearings having very tight tolerances mustbe used to support and hold the rotor in place. Also, the housingmaterials supporting the stator must be able to withstand these veryhigh axial forces without deforming over the life of the device.Furthermore, since the stator and rotor supporting members are membersthat are substantially disk shaped and are generally planar, they aremore susceptible to warping or deformation due to the large axialmagnetic forces and due to internal stresses caused by temperaturechanges that occur regularly during normal operation of the device. Aslarger and larger axial gap devices are contemplated, the magneticforces between the rotor and stator become larger and larger furthercompounding this problem.

The present invention provides improved methods and arrangements forproviding electric motors, generators, and regenerative motors that usemagnetic cores formed from thin film soft magnetic core materials. Thepresent invention also provides for improved electric motor, generator,and regenerative motor configurations that more fully utilize thepotential benefits associated with using magnetic cores formed from thinfilm soft magnetic materials.

SUMMARY OF THE INVENTION

As will be described in more detail hereinafter, magnetic cores for useas part of a stator arrangement in a device such as an electric motor,an electric generator, or a regenerative electric motor are disclosedherein. Stator arrangements and methods of making stator arrangementsutilizing the magnetic cores, and devices and methods of making devicesutilizing the stator arrangements, are also disclosed. The devices andstator arrangements include a plurality of independent energizableelectromagnetic assemblies with each independent electromagneticassembly including an associated one-piece magnetic core formed fromthin film soft magnetic material. Each independent electromagneticassembly defines two stator poles located at opposite ends of theone-piece magnetic core. Each one-piece magnetic core provides theentire magnetic return path for the two opposite magnetic stator polesassociated with each independent electromagnetic assembly.

In one embodiment, the device is a radial gap device and the magneticcore formed from thin film soft magnetic material is U-shaped with thestator poles being located at the ends of the legs of the U-shapedmagnetic core. In one version of this embodiment, the thin film softmagnetic material is a nano-crystalline material. In accordance withanother aspect of the invention, each of the independent electromagneticassemblies may be independently removed and replaced. Also, the devicemay be a multiple-phase device and the device may be a switchedreluctance device, an induction device, or a permanent magnet device.

In another embodiment, the device is a high frequency device. In thisembodiment, the device includes a rotor arrangement supported forrotation about a given rotational axis at a certain range of normaloperating rotational speeds. The rotor arrangement includes a pluralityof rotor poles for magnetically interacting with the stator poles. Therotor poles are supported for rotation about the rotational axis along acircular path. The device further includes a switching arrangement forcontrolling the electromagnetic assemblies. The switching arrangement isconfigured such that the switching arrangement is able to cause thestator poles of the electromagnetic assemblies to magnetically interactwith the rotor poles of the rotor arrangement at a frequency of at least500 cycles per second while the device is operated within at least aportion of the normal operating rotational speed range. In one versionof this embodiment, the number of rotor poles is such that the switchingarrangement causes the stator poles of the electromagnetic assemblies tomagnetically interact with the rotor poles of the rotor arrangement suchthat the ratio of the frequency of the device in cycles per secondrelative to the revolutions per minute of the device is greater than 1to 4 during the operation of the device.

In another embodiment, the device is a radial gap device and theelectromagnetic assemblies include U-shaped, one-piece magnetic coresformed such that the stator poles of each electromagnetic assembly arelocated at the ends of the legs of the U-shaped magnetic cores. Theelectromagnetic assemblies are positioned around the circular path ofthe rotor poles. Each electromagnetic assembly is positioned such thatthe two stator poles of each electromagnetic assembly are locatedadjacent to one another and in line with one another along a line thatis parallel with the rotational axis of the device. In one version ofthis embodiment, the rotor poles are pairs of rotor poles formed fromadjacent pairs of permanent magnet segments configured to form rotorpoles of opposite magnetic polarity. Each pair of permanent magnetsegments is positioned such that the two permanent magnet segments arelocated adjacent to one another and in line with one another along aline that is parallel with the rotational axis of the device such thatthe two permanent magnet segments define two adjacent circular pathsaround the rotational axis of the device when the rotor is rotated aboutthe rotational axis of the device. Each of the two adjacent circularpaths faces an associated one of the stator poles of eachelectromagnetic assembly. In this version, the rotor arrangementincludes at least 36 pairs of adjacent rotor poles and the statorarrangement includes at least 48 electromagnetic assemblies. The statorpoles may be arranged to face inward toward the rotational axis of thedevice, or alternatively, may be arranged to face outward away from therotational axis of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1 is a diagrammatic cross-sectional plan view of a device designedin accordance with the present invention including a rotor arrangementand a stator arrangement having a plurality of electromagneticassemblies.

FIG. 2 is a cross-sectional view of the device of FIG. 1 taken throughsection line 2—2 of FIG. 1.

FIG. 3 is a diagrammatic cross-sectional plan view of another embodimentof a device designed in accordance with the present invention includinga rotor arrangement and a stator arrangement having a plurality ofelectromagnetic assemblies.

FIG. 4 is a cross-sectional view of the device of FIG. 3 taken throughsection line 4—4 of FIG. 3.

FIG. 5 is a diagrammatic side view of a thin film soft magnetic materialwinding used to form one-piece magnetic cores in accordance with theinvention.

FIG. 6 is a diagrammatic plan view of two configurations of statorpoles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning to the drawings, wherein like components are designated by likereference numerals throughout the various figures, attention isinitially directed to FIGS. 1 and 2. FIG. 1 illustrates a crosssectional plan view of a device 100 designed in accordance with thepresent invention. Although device 100 will be referred to as anelectric motor or an electric generator at various times throughout thisdescription, it should be understood that device 100 may take the formof a motor, a generator, an alternator, or a regenerative motordepending on the requirements of the application in which the device isused. For purposes of this description, the term regenerative motorrefers to a device that may be operated as either an electric motor oran electric generator.

Also, although device 100 will in most cases be described as a DCbrushless motor, it should be understood that it may take the form of awide variety of other types of motors and/or generators and still remainwithin the scope of the invention. These other types of motors and/oralternators/generators include, but are not limited to, DC synchronousdevices, variable reluctance or switched reluctance devices, andinduction type motors. The specific differences between these differenttypes of devices are well known to those skilled in the art andtherefore will not be described in detail. For example, although device100 will in most cases be described as a DC brushless motor that usespermanent magnets as rotor poles, it should be understood that the rotorpoles would not be permanent magnets in the case of a switchedreluctance device or an induction device. Instead, the rotor poles ofthese types of devices would most likely be provided by protrusions ofother magnetic materials formed from laminations of materials such asiron or preferably thin film soft magnetic materials such as those thatwill be described hereinafter with reference to the stator corematerials of the present invention.

As best shown in FIG. 1, device 100 includes a rotor arrangement 102 anda stator arrangement 104. In this embodiment, device 100 takes the formof a hub motor/generator with rotor arrangement 102 being located aroundthe outer perimeter of device 100. Stator arrangement 104 is locatedinside of rotor arrangement 102. As best shown in FIG. 2, which is across sectional view of a portion of device 100 as indicated by section2-2 of FIG. 1, rotor arrangement 102 is supported by bearings 110 sothat rotor arrangement 102 may rotate around stator arrangement 104. Anair gap 108 separates rotor arrangement 102 from stator arrangement 104.

Although device 100 is illustrated using bearings 110 for supportingrotor arrangement 102 for rotation about stator arrangement 104 and axis106, this is not a requirement. Instead, it should be understood thatany other suitable and readily providable arrangement for supportingrotor arrangement 102 may be utilized and still remain within the scopeof the invention. Also, although device 100 has been described as a hubmotor/generator, this is not a requirement of the invention. Instead, aswill be described in more detail hereinafter, the device may be any typeof electric motor, generator, or regenerative motor so long as thedevice includes a stator arrangement that has a plurality ofelectromagnets having magnetic cores formed from a thin film softmagnetic material with the electromagnets being configured in accordancewith the invention.

Referring to both FIGS. 1 and 2, rotor arrangement 102 will now bedescribed in more detail. In this embodiment, device 100 is a radial gaptype device and rotor arrangement 102 includes 48 pairs of radiallyadjacent permanent magnet segments 112. Magnet segments 112 may be supermagnets such as cobalt rare earth magnets or any other suitable orreadily providable magnet material. Each of the 48 magnet segment pairs112 includes a first magnet segment oriented to form a north rotor pole112 a and a second magnet segment oriented to form a south rotor pole112 b. As illustrated in FIG. 2, north rotor pole 112 a is locatedadjacent to south rotor pole 112 b such that the two permanent magnetsegments are in line with one another along a line that is parallel withthe rotational axis of the device. With this orientation, the twopermanent magnet segments 112 a and 112 b of each magnet segment pair112 define two adjacent circular paths around rotational axis 106 ofdevice 100 when the rotor arrangement is rotated about the rotationalaxis of the device. As shown best in FIG. 1, the 48 magnet pairs arepositioned around the inside periphery of rotor arrangement 102 facingair gap 108 with each consecutive pair being reversed such that all ofthe adjacent magnet segments alternate from north to south around theentire rotor arrangement in both of the circular paths defined by thepairs of magnet segments 112.

Although magnets 112 have been described as being permanent supermagnets, this is not a requirement. Alternatively, the magnets may beother magnetic materials, or, in some cases may be electromagnets. Also,although the rotor has been described as including 48 magnet pairs, itshould be understood that the rotor may include any number of magnetpairs and still remain within the scope of the invention. And finally,although the rotor arrangement has been described as including magnets,this is not a requirement. For example, in the case of a switchedreluctance motor or an induction motor, rotor arrangement 102 would notinclude magnets at all. Instead, as would be understood by those skilledin the art, rotor arrangement 102 would be constructed from an ironbased material or some other magnetic material such as thin film softmagnetic material to form a magnetic rotor core which would be driven bya rotating magnetic field created by the switching of the statorarrangement.

In this embodiment, stator arrangement 104 includes 48 independentelectromagnetic assemblies 114. Each electromagnetic assembly 114includes an associated one-piece magnetic core 116 formed from anano-crystalline, thin film soft magnetic material and a pair of coils118. As shown best in FIG. 2, each one-piece magnetic core 116 isU-shaped with coils 118 being positioned around the legs of U-shapedmagnetic core 116. With this configuration, each independentelectromagnetic assembly defines two stator poles 120 a and 120 blocated at opposite ends of the one-piece magnetic core. Theelectromagnetic assemblies 114 are positioned around the circular pathof the rotor poles as shown in FIG. 1. As shown best in FIG. 2, eachelectromagnetic assembly 114 is positioned such that the two statorpoles 120 a and 120 b of each electromagnetic assembly are locatedadjacent to one another and in line with one another along a line thatis parallel with the rotational axis of the device. This places the twostator poles of each electromagnetic assembly facing air gap 108 and ina confronting relationship with magnet segment pairs 112 a and 112 b.

Although magnetic cores 116 have been described as being formed from anano-crystalline, thin film soft magnetic material, this is not arequirement of the invention. Instead, any thin film soft magneticmaterial may be used. These materials include, but are not limited to,materials generally referred to as amorphous metals, materials similarin elemental alloy composition to nano-crystalline materials that havebeen processed in some manner to further reduce the size of thecrystalline structure of the material, and any other thin film materialshaving similar molecular structures to amorphous metal andnano-crystalline materials regardless of the specific processes thathave been used to control the size and orientation of the molecularstructure of the material.

Also, although electromagnetic assemblies 114 have been described asincluding a pair of coils located on the legs of the U-shaped magneticcore 116, this is not a requirement of the invention. Instead, the coilsmay be a single coil located at the base of the U-shaped magnetic core,a single coil running along the entire length of the core, or any otherdesired configuration using one or more coils. As illustrated in FIG. 1,the coils may be tapered coils with more windings at one end of each legof the U-shaped core. This configuration allows the larger number ofwindings at one end to more fully fill the larger spaces left betweenthe magnetic cores in the regions that are further away from therotational axis. Furthermore, these coils may be wrapped directly ontothe core pieces, or alternatively, the coils may be formed separatelyfrom the core pieces, wrapped with insulation or otherwise insulated,and then slipped over the core during the assembly of theelectromagnetic assembly.

In accordance with one aspect of the invention, each one-piece magneticcore 116 provides the entire magnetic return path for the two oppositemagnetic stator poles 120 a and 120 b associated with each independentelectromagnetic assembly 114. This configuration eliminates the need fora traditional style back iron of magnetic core material thatmagnetically interconnects all of the stator poles. By eliminating therequirement for a back iron that is common to all of the stator poles,the weight of the device may be reduced compared to the weight of asimilarly sized device that utilizes a more conventional configurationthat includes a common back iron for magnetically interconnecting thestator poles.

Electromagnetic assemblies 114 may be mechanically held in positionusing any conventional manner for holding elements in place. Forexample, electromagnetic assemblies 114 may all be potted orencapsulated into one complete overall stator using an encapsulatingmaterial such as a thermally conductive, dielectric epoxy. However, eachelectromagnetic assembly may be individually encapsulated into a wedgeshaped piece such as wedge shaped piece 122 shown in FIG. 1. These wedgeshaped pieces may then be assembled into an overall stator using a diskshaped structural element such as elements 124 in FIG. 2 located on eachside of the electromagnetic assemblies to support pieces 122.Alternatively, any other suitable and readily providable arrangement forsupporting wedge shaped pieces may be used and still fall within thescope of the invention.

Because each of the electromagnetic assemblies 114 may be provided as anindependent assembly including its own one-piece magnetic core thatprovides the entire return path for the associated stator poles of theelectromagnetic assembly, these assemblies may be configured such thatthey are easily removable and replaceable. For example, as describedabove, each electromagnetic assembly may be independently encapsulatedand then assembled into an overall stator. This allows any givenelectromagnetic assembly to be relatively easily removed and replaced.This ability to relatively easily replace the individual electromagneticassemblies improves the serviceability of the device. Also, this modularapproach allows a particular electromagnetic assembly configuration tobe used in a variety of specific device designs thereby potentiallyimproving the economies of scale that may be obtained using thisapproach.

Although the electromagnetic assemblies have been described as beingencapsulated, this is not a requirement of the invention. Instead, theelectromagnetic assemblies may be assembled and then simply clamped intoposition without being encapsulated. Therefore, it should be understoodthat any known method may be used to support the electromagneticassemblies in their respective locations.

As described above, device 100 includes 48 electromagnetic assembliesdefining 48 pairs of stator poles. Device 100 also includes 48 pairs ofmagnet segments that define a corresponding 48 pairs of rotor poles. Inthis embodiment, stator arrangement 104 is wired as a single-phasedevice. That is, every electromagnetic assembly is wired together inseries, as indicated in FIG. 1 by wires 126. Also, this device has astator pole to rotor pole ratio of 1 to 1. Although this embodiment isdescribed as a single-phase device having a 1 to 1 stator pole to rotorpole ratio, this is not a requirement. Instead, the device may be amulti-phase device or a device having any desired stator pole to rotorpole ratio.

Although device 100 has been described with the rotor arrangement aroundthe outer perimeter of the device and the stator arrangement locatedinside of the rotor arrangement, this is not a requirement. Instead, thestator arrangement may be located around the outer perimeter of thedevice with the rotor arrangement inside of the stator arrangement asillustrated in FIGS. 3 and 4. These figures illustrate a device 300having a rotor arrangement 302 and a stator arrangement 304. Statorarrangement 304 includes 48 electromagnetic assemblies 306 that usemagnetic cores 116 that are identical to those used in device 100 exceptthat they are oriented in the opposite direction as shown best in FIG.4. Each electromagnetic assembly 306 also includes coils 308. Coils 308are similar to coils 118 of device 100 except that they are tapered inthe opposite direction so that there are more windings at the base ofeach of the legs of U-shaped magnetic core 116. This allows the windingsto more fully fill the larger spaces available at the bases of theU-shaped legs compared to the ends of the U-shaped cores due to theirinwardly facing orientation. For illustrative purposes, device 300 isset up as a 4-phase device having a stator pole to rotor pole ratio of 4to 3. As shown in FIG. 3, wires 310 connect every fourth electromagneticassembly in series to create 4 groupings of 12 electromagneticassemblies making the device a 4-phase device. Also, rotor arrangement302 includes only 36 pairs of rotor magnet segments rather than the 48pairs described for device 100. As is well known in the art, this typeof configuration reduces the detent effect that is prevalent insingle-phase devices and it delivers a torque more consistentlythroughout the rotation of the device compared to a single phase device

Referring now to FIG. 5, the specific configuration of magnetic core 116for the particular embodiments shown in FIGS. 1-4 will be described inmore detail. Each individual one-piece magnetic core 116 is formed bywinding a continuous ribbon of thin film soft magnetic material into adesired shape. In the case of core 116, the shape is a generally ovalshape as indicated by winding 500 in FIG. 5. Since thin film softmagnetic materials such as amorphous metal or nano-crystalline materialsare typically provided in very thin tape form (for example, less than 1mil thick), winding 500 may be made up of hundreds of winds of material.Once wound into the desired shape, winding 500 may be annealed toproduce the desired magnetic characteristics and then saturated andencapsulated with a thin layer of adhesive material. Once annealed,these materials are very hard and typically very brittle making themsomewhat difficult to machine. In the embodiment shown in FIG. 5,winding 500 is then cut into two U-shaped pieces that each provide oneof the one-piece magnetic cores 116 described above.

As described above, one advantage to this configuration is that, whenassembled into an electromagnetic assembly as described above, eachone-piece magnetic core provides the entire return path for the twostator poles formed by the legs of the U-shaped magnetic core. Thiseliminates the need for a back iron to magnetically interconnect each ofthe stator poles. Another advantage to this configuration is that thereare no parasitic gaps within the one-piece magnetic cores. Also, thisconfiguration orients the layers of thin film soft magnetic material inthe proper orientation for directing the flux through the magnetic core.

Although the core pieces have been described as being wound from acontinuous ribbon of thin film soft magnetic material, this is not arequirement. Alternatively, the magnetic cores may be formed by stackingindividually formed strips of material to form a magnetic core of anydesired shape. Furthermore, the individual strips may be stacked atopone another with each piece being the same size and shape, or,alternatively, the individual strips may be stacked beside one anotherwith various individual pieces having different sizes and shapes. Thesevarious approaches allow a wide variety of specific shapes to be formed.

As is known to those skilled in the art, when thin filmed soft magneticmaterial is annealed, it can have a particular direction along whichmagnetic flux will be directed most efficiently. For a ribbon of thinfilm soft magnetic material, this direction is typically either alongthe length of the ribbon or across the width of the ribbon. By using theappropriate approach described above to form each of the magnetic cores,the magnetic cores may be formed such that the material is alwaysoriented such that the magnetic flux is directed through the piecesalong the direction of the material that most efficiently directs themagnetic flux.

Devices 100 and 300 also include a switching arrangement 550, shown inFIGS. 1 and 3, for activating and deactivating coils 118 and coils 308respectively with alternating polarity. Switching arrangement 550 may beany suitable and readily providable controller that is capable ofdynamically activating and deactivating electromagnetic assemblies 114and 306. Preferably, switching arrangement 550 is a programmablecontroller capable of activating and deactivating the electromagneticassemblies at a rate of speed much higher than is typically done inconventional electric motors and generators. This is because of theinherent speed at which the magnetic field may be switched in a thinfilm soft magnetic core.

In accordance with another aspect of the invention, devices 100 and 300include a very high pole count stator and rotor arrangement. As will nowbe described in more detail, this high pole count configuration providesseveral substantial and unexpected benefits compared to prior artmotors/generators that use magnetic cores formed from thin film softmagnetic materials. As indicated in the prior art patents cited in thebackground of the invention, prior art devices utilizing magnetic coresformed from amorphous metal films have been described. However, thesemotors have been described as low pole count motors that use the highfrequency capabilities of the amorphous metal material to provide veryhigh rotational speed motors. The present invention takes advantage ofthe high frequency capabilities in a novel way. Instead of using thehigh frequency to produce high rotational speed, the present inventioncombines the high frequency capabilities of a magnetic core formed fromthin film soft magnetic material with extraordinarily high pole counts.This combination provides devices capable of very high power densitieswhile maintaining very manageable rotational speeds.

Although prior art devices may be capable of achieving relativelycomparable overall power densities compared to those described herein,they obtain the high power output by providing a very high rotationalspeed device. This means that for many applications in which the highrotational speed is not desired, reduction gears must be used causingthe overall system that uses the reduction gear to lose efficiency. Inmany situations, a device designed in accordance with this aspect of theinvention, eliminates the need for reduction gears altogether therebyimproving the overall efficiency of the system using the device.Furthermore, since the devices of the invention are able to deliver thehigh power densities while operating at much lower rotational speedsthan previously contemplated, these devices are not subjected to theextreme centrifugal forces generated by much higher rotational speeddevices. This makes devices in accordance with the invention much morereliable and economical to manufacture compared to high rotational speeddevices.

In addition to the advantage of providing very high power density atrelatively low rotational speeds, devices designed in accordance withthe present invention provide another unanticipated benefit. Assumingthat the linkage area is held constant, that is, assuming that theactual physical area that exists between the stator poles and the rotorpoles is held constant, increasing the pole count actually reduces theamount of material needed to provide the overall electromagneticassemblies. This is illustrated in FIG. 6, which is a diagramillustrating plan views of two different stator pole configurations. Onthe left, a square shaped stator pole arrangement 600 includes a statorpole 602 and a winding 604 surrounding the stator pole perimeter. On theright of FIG. 6, the stator pole arrangement 606 includes 4 narrowerrectangular shaped poles 608 a-d and associated windings 610 a-dsurrounding each stator poles perimeter. In this example, the area ofstator pole 602 is equal to the total area of stator poles 608 a-d.However, each of windings 610 a-d of arrangement 606 only need to haveone quarter of the windings compared to windings 604 in order to providethe some overall flux linkage as stator pole arrangement 600 since eachwinding 610 a-d only needs to generate one quarter of the flux linkage.

As illustrated in FIG. 6, the overall width W of both arrangement 600and 606 is the same. Also, the area, and therefore the volume, of thewindings along the sides of the stator poles of both arrangements is thesame as indicated by the cross hatched portions of the windings of thetwo arrangements. However, as clearly shown in FIG. 6, the thickness T2,and therefore the area and volume, of the windings above and below thestator poles in arrangement 606 is reduced to one quarter the thicknessT1 of arrangement 600. This significantly reduces the weight of theoverall material cost associated with the device. Also, if the device isa device that includes a back iron for magnetically interconnecting thestator poles to provide a return path for the flux, the requiredthickness of the back iron is also reduced by a factor of four since thearea of each stator pole is reduced by a factor of four. Since thesehigh pole count devices provide the same torque as low pole countdevices having the same linkage area, these reductions in the amount ofmaterial required has the potential to significantly reduce the weight,size, and material cost associated with the higher pole count device.

Now that the general approach to designing a high frequency/high polecount device in accordance with the invention has been described, ofspecific examples will be described to more clearly point out theadvantages of this approach. In a first example, a permanent magnetmotor having the configuration described above with reference to FIGS. 1and 2 will be described. This configuration places the rotor out nearthe outer perimeter of the device which provides the largest possibletorque arm for a given size device.

In this first example, the motor is designed to have an overall diameterof about 8 inches and an overall width of about 4 inches. Also, 48 pairsof magnet segments are used to form the rotor poles and 48electromagnetic assemblies are used. Each U-shaped core piece is formedusing nano-crystalline material having a tape width of 0.150 inchesthereby giving the one-piece, U-shaped magnetic core an overallthickness of about 0.150 inches. For this example, the overall U-shapedmagnetic core is approximately 2¼ inches wide and 1¾ inches tall witheach leg of the U-shaped core protruding about ¾ of an inch from thebase of the U-shaped core and a space of about ¼ inch between the twolegs of the U-shaped core. This configuration results in two statorpoles that are ¾ of an inch long and that have a stator pole face areaabout 1 inch wide by 0.150 inches thick. In this example, coils areformed on each leg of the U-shaped core by winding two layers of18-gauge wire over each leg along the entire ¾ inch length of the legs.This results in a winding thickness of about {fraction (1/16)} of aninch. Super magnets are used to form the rotor poles with each magnetsegment being approximately {fraction (3/16)} of an inch thick and 1inch wide with each magnet segment having a magnet span of about ⅓ of aninch along the direction of the rotational path of the rotor. Thisconfiguration results in an overall device that has a 3½ inch torque armand weighs only about 20 pounds.

Because the device described above uses a thin film soft magneticmaterial to form the stator cores, this device is designed to operatevery efficiently at frequencies of up to at least 1500 Hz. Also, since48 pairs of magnets are used with each circular path having 48 magnetsegments that alternate in polarity from north to south, the device willgo through 24 cycles for each rotation of the rotor. Therefore, whenoperating at 1500 cycles per second, the device will be rotating at arate of 62½ revolutions per second or 3750 RPM. This results in a veryhigh frequency (1500 Hz) to RPM (3750) ratio of 0.4 which issubstantially greater than prior art devices. This ratio of frequency toRPM is an easy ratio to determine and is a ratio that may be used todifferentiate devices designed in accordance with the invention fromprior art devices.

Based on proven magnetic modeling methods and based on tests resultsfrom specific components and devices built in accordance with theinvention, a motor built to the specifications described above isexpected to provide the following performance characteristics. Asmentioned above, the motor operates in a frequency range of 0-1500 Hzand rotates at speeds in the range of 0-3750 RPM. Also, the motor onlyweighs about 20 pounds. The peak torque is expected to be about 70foot-pounds with a continuous torque of about 50 foot-pounds. The peakhorsepower is expected to be about 53 HP at 3750 RPM and the motor isexpected to produce a continuous horsepower output of about 35 HP at3750 RPM. As can be seen by these results, devices designed inaccordance with the invention are capable of very high power densities.

Although the devices described above have been described as having 48magnet pairs and 48 electromagnetic assemblies, this is not arequirement. In fact, the preferred embodiment of the invention forcertain applications may utilize much higher pole counts in largerdiameter devices. For example, in the case of a motor that is designedin accordance with the invention and that is designed to be used as ahub motor to directly drive the wheel of a vehicle, the overall diameterof the motor may be substantially larger and the number of magnets andelectromagnets may be much greater. In order to illustrate this point, apreferred embodiment of a hub motor for driving a vehicle wheel will bebriefly described.

In this embodiment, the hub motor will be designed to have an overalldiameter of 15 inches, which is a common vehicle wheel size. Based onthis wheel size, this embodiment of the direct drive hub motor will bedesigned to operate at about 1500 RPM since this would provide anappropriate top speed for the vehicle given the wheel size. Also, asdescribed above, the motor will be designed to operate within afrequency range of 0-1500 Hz. Given these parameters, the motor willhave a frequency to RPM ratio of 1 to 1. Again, this ratio of frequencyto rotational speed is much higher than conventional motors. Also, sincethe ratio of frequency to RPM is 1 to 1 for this device, the device willneed to go through 60 cycles per revolution and will require a polecount of 120 rotor poles, and in this case 120 electromagneticassemblies since this device is being described as a single phase devicefor purposes of simplicity. Using the same basic design as describedabove for the 8-inch motor and device 100 of FIG. 1, the 120 magnetpairs would be distributed around the outer perimeter of the motor andthe 120 electromagnetic assemblies would be positioned in an outwardlyfacing orientation facing the rotor magnets. This configuration wouldprovide a torque arm of about 7 inches, or twice that described for the8-inch motor. Also, since the thickness of each electromagnetic assemblyis less than ⅓ of an inch and the circumference of the device at the airgap between the rotor and the stator is about 44 inches, there is roomfor 120 electromagnetic assemblies that are the exact same size andconfiguration as described above for the 8-inch motor.

By scaling up the design as described above, the larger 15-inch devicewould provide the following performance characteristics. As mentionedabove, the motor operates in a frequency range of 0-1500 Hz and rotatesat speeds in the range of 0-1500 RPM. Also, the motor would weigh about50 pounds. The torque would be about five times that of the 8-inchmotor, which would give a peak torque of 350 foot-pounds with acontinuous torque of about 250 foot-pounds. This is because the torquearm is doubled from 3½ inches to 7 inches and because the number ofelectromagnets goes from 48 to 120. Therefore the torque is increased bya factor of 2 times 120/48, which equals 5. The peak horsepower would beabout 100 HP at 1500 RPM and the motor would produce a continuoushorsepower of about 71 HP at 1500 RPM.

When comparing devices designed in accordance with the presentinvention, the ratio of frequency to RPM provides an easy distinguishingcharacteristic. For example, the vast majority of currently availablemotors are designed to operate at 50 to 60 Hz. The main reason for thisis that these are the frequencies available on AC electrical powergrids. However, another reason for this, and one of the reasons AC poweris provided at this frequency, is that these frequencies are well withinthe frequency capabilities of a conventional iron core motor. Thesemotors are also most often designed to operate at rotational speeds ofaround 1800 RPM. This gives these types of motors a frequency to RPMratio of 60 to 1800 or 0.03.

Even in the case of specialty iron core motors, the frequenciestypically remain below 400 Hz. This is because the iron core materialsimply cannot respond to the changing fields this quickly withoutcausing very large losses that show up in the form of heat. Therefore,in order to keep the frequencies of conventional motors and generatorslow, these devices have historically been designed with relatively lowpole counts. As new materials were developed that could operate athigher frequencies, such as amorphous metals, the tendency was to usethe new materials in conventional motor designs. This allowed thesedevices that used the new high frequency materials to operate at muchhigher RPM. However, the present invention provides a new approach todesigning devices using high frequency materials. Instead of using thehigh frequency material to allow higher speed devices, the presentinvention combines the high frequency capabilities with dramaticallyhigher pole counts to provide devices that have a frequency torotational speed ratio that is higher than prior art devices. Forexample, devices designed in accordance with the present invention willhave a frequency to rotational speed ratio greater than 1 to 4 whenfrequency is measured in cycles per second and rotational speed ismeasured in RPM. This high frequency to rotational speed ratio ofgreater than 0.25 provides high stall torque devices that are capable ofvery high power densities yet still operate at very manageablerotational speeds.

Although the above described embodiments have been described with thevarious components having particular respective orientations, it shouldbe understood that the present invention may take on a wide variety ofspecific configurations with the various components being located in awide variety of positions and mutual orientations and still remainwithin the scope of the present invention. For example, although eachstator arrangement was described as including a certain number of statorpoles and the rotor was described as including a certain number of rotorpoles, this is not a requirement. Instead, the stator arrangement mayhave any desired number of stator poles and the rotor any number ofrotor poles and still remain within the scope of the invention.

Additionally, the present invention would equally apply to a widevariety of electric motors and generators so long as the statorarrangement of the device includes a plurality of electromagneticassemblies with each assembly having a one-piece core formed from thinfilm soft magnetic material that provides the entire return path for thestator poles of that assembly. Or, alternatively, the present inventionwould equally apply to a wide variety of electric motors and generatorsso long as the device includes a stator arrangement having a magneticcore formed from a thin film soft magnetic core material and operateswith a frequency to rotational speed ratio of greater than 1 to 4. Thesevarious generators and motors include, but are not limited to, motorsand generators of the DC brushless type, DC synchronous type, variablereluctance or switched reluctance type, induction type, and many othertypes of generators, motors, and alternators. These various devices alsoinclude single-phase devices and multi-phase devices. Therefore, thepresent examples are to be considered as illustrative and notrestrictive, and the invention is not to be limited to the details givenherein, but may be modified within the scope of the appended claims.

1. A method of making a device selected from the group of devicesconsisting of an electric motor, an electric generator, and aregenerative electric motor, the method comprising the steps of:providing a plurality of independent energizable electromagneticassemblies with each independent electromagnetic assembly including anassociated one-piece magnetic core formed from thin film soft magneticmaterial, each independent electromagnetic assembly defining two statorpoles located at opposite ends of the one-piece magnetic core, andassembling the independent electromagnetic assemblies into at least onestator arrangement in such a way that each one-piece magnetic coreprovides the entire magnetic return path for the two opposite magneticstator poles associated with each independent electromagnetic assembly.2. A method according to claim 1 wherein the device is a radial gapdevice.
 3. A method according to claim 1 wherein each of the one-piecemagnetic cores is U-shaped with the stator poles being located at theends of the legs of the U-shaped magnetic core.
 4. A method according toclaim 1 wherein the thin film soft magnetic material is anano-crystalline material.
 5. A method according to claim 1 wherein eachof the independent electromagnetic assemblies is independently removableand replaceable.
 6. A method according to claim 1 wherein the device isa device selected from the group of devices consisting of a switchedreluctance device, an induction device, or a permanent magnet device. 7.A method according to claim 1 wherein the device is a rotating deviceand the method includes the step of assembling a rotor arrangementsupported for rotation about a given rotational axis at a certain rangeof normal operating rotational speeds, the rotor arrangement including aplurality of rotor poles for magnetically interacting with the statorpoles, the rotor poles being supported for rotation about the rotationalaxis along a circular path.
 8. A method according to claim 7 wherein themethod further includes the step of providing a switching arrangementfor controlling the electromagnetic assemblies, the switchingarrangement being configured such that the switching arrangement is ableto cause the stator poles of the electromagnetic assemblies tomagnetically interact with the rotor poles of the rotor arrangement at afrequency of at least 500 cycles per second while the device is operatedwithin at least a portion of the normal operating rotational speedrange.
 9. A method according to claim 8 wherein the number of rotorpoles is such that the switching arrangement causes the stator poles ofthe electromagnetic assemblies to magnetically interact with the rotorpoles of the rotor arrangement such that the ratio of the frequency ofthe device in cycles per second relative to the revolutions per minuteof the device is greater than 1 to 4 during the operation of the device.10. A method according to claim 7 wherein the device is a radial gapdevice, the electromagnetic assemblies include U-shaped one-piecemagnetic cores formed such that the stator poles of each electromagneticassembly are located at the ends of the legs of the U-shaped magneticcores, and the step of assembling the stator arrangement includesassembling the stator arrangement such that the electromagneticassemblies are positioned around the circular path of the rotor poleswith each electromagnetic assembly being positioned such that the twostator poles of each electromagnetic assembly are located adjacent toone another and in line with one another along a line that is parallelwith the rotational axis of the device.
 11. A method according to claim10 wherein the rotor poles are pairs of rotor poles formed from adjacentpairs of permanent magnet segments, and the step of assembling the rotorarrangement includes configuring the pairs of rotor poles to form rotorpoles of opposite magnetic polarity, each pair of permanent magnetsegments being positioned such that the two permanent magnet segmentsare located adjacent to one another and in line with one another along aline that is parallel with the rotational axis of the device such thatthe two permanent magnet segments define two adjacent circular pathsaround the rotational axis of the device when the rotor is rotated aboutthe rotational axis of the device, each of the two adjacent circularpaths facing an associated one of the stator poles of eachelectromagnetic assembly.
 12. A method according to claim 11 wherein therotor arrangement includes at least 36 pairs of adjacent rotor poles.13. A method according to claim 10 wherein the stator arrangementincludes at least 48 electromagnetic assemblies.
 14. A method accordingto claim 10 wherein the stator poles face inward toward the rotationalaxis of the device.
 15. A method according to claim 10 wherein thestator poles face outward away from the rotational axis of the device.16. A method according to claim 1 wherein the device is a multiple phasedevice.